They usually make it so you can’t cash out anything that’s less than the voucher. Or rather that the wins get counted first.
Let’s say you get $50 free, win $25. You then play for $25 and lose, the remaining $25 shown on your balance won’t be able to be cashed out.
And if you get poisoned with 2,4-DNP, your ATP will make you into a thermal power plant before you die of uncontrolled hyperthermia!